1. Field of the Invention
The invention relates to a control system for a poly-chromatic light-emitting diode (LED) lighting system, particularly to a control system for a poly-chromatic light-emitting diode lighting system with lighting forward and junction temperature feedback control.
2. Description of the Prior Art
The Light Emitting Diode (LED) has many advantages, such as small volume, high lighting efficiency, quick response speed, long life, low power consumption, and so on. It can be used to replace the traditional lighting bulbs and lamps which are of high power consumption, short utilization life, and high pollution. Thus, the LED has already been applied as the new-generation lighting equipments.
The LED is also applied as the white light sources. That is, the red, green, and blue lights (or more than three lights) are mixed to form white light. Because the spectrum of natural white light is ranged from about 400 nm to 720 nm, the synthetic white light can consist of the red, green and blue (RGB) lights or more than three lights. Similarly, the poly-chromatic light can be synthesized by three (red, green, blue) or more than three LED lights. However, the spectrum of LED is influenced by the input power and the junction temperature. Therefore, when the electrical power or the junction temperature is changed, the spectrum of poly-chromatic LED will also be changed, and the luminance and color (related color temperature) of the output light will be influenced. Therefore, it is difficult to control the luminance and color of LED. Hence, it is very urgent to obtain the control device and method of poly-chromatic LED at present.
As for the example of a conventional three-chromatic LED lighting system, the model of LED lighting systems is nonlinear and time-varying. Most conventional well-known systems use the open-loop control or simple closed-loop control, which is not effective in that the luminance and color of lighting source will drift, and the LED system cannot achieve good performance.
For example, Taiwan Patent No. 200723194 related to a LED lighting system, which is used to produce poly-chromatic LED lighting sources, and the difference between the set point value and first control data is used to control the LED lighting sources. It uses the filtering-type photodiode as the color sensor, and evaluates the junction temperature by the temperature sensor and the thermal resistance of LED. In addition, U.S. Pat. No. 7,573,210 relates to a lamp system and a method for feedback control. The system discloses a lamp with the chromaticity and the digital output signals. The lamp contains spectrum filtering elements and light sensors for providing optical feedback, such that the unnecessary optical signals can be removed and filtered. The control system can sample the filtered signals according to the preset feedback sampling spectrum, and control the chromatic output according to the feedback signals. However, the measurement of LED junction temperature is not disclosed for control of luminance. Furthermore, both afore-mentioned patents do not disclose the use of “non-filtering-type photodiodes” as light sensors for detecting color, and the direct measure of junction temperature of LED for luminance and color control.
Therefore, in order to produce more effective LED, it is necessary to research and develop innovative LED technology, and then to stabilize the luminance and color of LED, and raise the efficiency of light sources, also, reduce the manufacturing time and the manufacturing cost.